Tomato Fusarium Wilt
Fusarium wilt disease has been reported in over 30 countries. It usually affects tomatoes in southern areas of the US and Europe. In more nothern, colder climates it is usually limited by low temperatures but it can wipe out greenhouse populations entirely. Luckily, you can take action to control and even prevent this dreadful disease.
Causes and Symptoms
Fusarium wilt in tomatoes is caused by the fungus Fusarium oxysporum f.sp. Lycopersici, which is soil borne and can survive indefinitely without any host. Most occurrances are associated with infected tomato debris left in the soil.
An infected tomato will begin yellowing on the bottom leaves. The yellowing will begin on one side of the leaf, shoot, or branch and then slowly spread out and up the vine. The vines will brown along the veins and eventually wilt permanently, resulting in a stunted plant. If the plant doesn’t die altoghether, it will be weak and produce inferior tomatoes.
Treatments and Control
There are a number of control measures that can be taken when dealing with a fusarium wilt.
One of the best ways to control this disease is to plant resistant varieties. These varietals are denoted with an “F” on the package or plants. Remember that resistant does not mean it will never get the disease, it is just much less likely.
Commercial growers sometimes steam or fumigate the soil to kill any fungus living there. For a home gardener, raising the pH of the soil to 6.5 – 7.0 can be just as effective as fumigation.
Use a nitrate-based nitrogen fertilizer, such as calcium nitrate, rather than an ammonia-based nitrogen fertilizer. This will help control the pathogen best.
A heavy mulch layer will keep the soil temperature low which can slow fungus growth. Keeping tomato plants weed-free will also help, since many weeds are hosts.
Rotate your crops! This won’t eliminate the disease completely, but it can help reduce losses. Be sure not to plant your tomatoes in the same spot more than once every four years.
For both home and commercial growers the utmost concern is cleanliness. Innoculum can spread through infected stakes, seeds, soil, equipment, tools, shoes, clothing, and even hands. Making sure to start your own seedlings in a fungus-free, sterile environment can go a long way in controlling infection.